Barium nitrate

Endpoint summary

Additional information

To cover the required aquatic toxicity endpoints, a read across approach is followed using data for barium chloride. In general, barium toxicity is believed to be predominantly caused by uptake of the free metal cation. The toxicity of the metal compound therefore depends in the first place on its capacity to release free metal cation to the environmental compartment under consideration. Next to compound-specific differences, the physicochemical properties of the environmental compartment typically also affect the relative abundance of the free metal cation and hence the magnitude of the adverse effect. It is clear that water solubility of a metal compound is one of the most important factors for taking into account differences in toxicity when performing read across. Both compounds, barium nitrate and barium chloride, are soluble metal compounds, therefore the use of ecotoxicity data available for barium chloride to cover endpoints for barium nitrate is justified. Although these barium compounds are considered very soluble in pure unbuffered water, the barium present in solution tends to precipitate to a large extent at environmentally relevant aquatic media due to formation of insoluble complexes with several ligands (e.g., sulfate, carbonate). This reduces the bioavailability of the metals and therefore limits aquatic toxicity. Aquatic toxicity tests with soluble barium compounds will therefore often yield unbound NOECs and effect concentrations. This was also the case for most reliable data available for the read across compound barium chloride (Gilberg, 2014; Egeler and Kiefer, 2010). The only bound values obtained originated from the study from Biesinger and Christensen (1972), yielding a 48-h EC50 of 14.5 mg Ba/L and a 21-d NOEC of 2.9 mg Ba/L. The use of unbounded NOEC values however can be considered in specific cases, e.g., when no other values are available for a particular species or when scientific evidence exist that the true toxicity towards a specific organism would be biased if such data were not taken into account. For example, if no effects were observed at the highest or the only tested concentration, then this concentration can be used as a conservative estimate for the “real” NOEC. The lowest unbound NOEC was the 72-h ErC50 for Pseudokirchneriella subcapitata (Egeler and Kiefer, 2010) of >= 1.15 mg dissolved Ba/L. This value will be used as key value for PNEC derivation for the aquatic compartment.